Typically, a modern helicopter rotor blade terminates inwardly at a longitudinally extending spindle which is concentrically received within an elastomeric bearing assembly carried within a rotatable hub. Large centrifugal loads generated by a rotating blade are carried through the spindle and into the bearing assembly.
In one known configuration, the blade spindle is attached to the elastomeric bearing assembly by a nut that is threaded onto an end of the spindle and attached longitudinally to an end of the bearing assembly by a plurality of bolts. A high precision fit between such threaded connectors (which may be difficult to achieve with reasonable economy) in such a spindle-bearing subassembly is necessary to control stress levels and stress distribution during operating conditions particularly along the thread of the nut and the spindle. Uneven stress distribution could increase the risk of mechanical failure of the spindle-bearing assembly.
It might be assumed that a threadless connector would be ideal for helicopter usage since threadless connectors eliminate the problem of the uneven loading a plurality of individual threads and are easily manufactured. To date, however, threadless connections have been found to be generally unsuited to accommodate the rigorous blade loading forces generated in helicopter usage. Typically, prior art threadless connections, as exemplified by U.S. Pat. Nos. 2,278,625 and 3,867,871, have a ring member that, upon assembly of the threadless connection, is driven into an annular groove in a spindle by a cooperating, surrounding loading hoop. As the ring is driven into the groove by the loading hoop, the ring cooperates with the spindle to locate the spindle in relation to a bearing. In order to properly locate the spindle against the bearing, the ring may be mechanically deformed by the driving action of the surrounding hoop. Any deformation may create weaknesses and uneven loading that could lead to failure.
The prior art generally fails to recognize that the threadless rings must be precisely located within the spindle grooves during centrifugal loading under operating conditions. An improperly located ring may cause uneven loading and wear that may lead to failure, particularly given the high loads encountered in helicopter operation. When a ring is driven into a groove, it is very difficult to ensure that the ring is precisely located within the spindle groove. By precisely locating the rings in the spindle grooves, wear and fretting is minimized and reliability against centrifugal load is maximized.
Accordingly, what is needed in the art is an improved threadless retention structure having an established relative position between a ring and a spindle prior to and after loading the ring against a bearing to minimize wear, uneven loading, fretting and concentrated stress caused by deformation. The retention structure should have a minimum number of parts, be highly reliable and be inexpensive to construct and maintain.